1. Field of the Invention
The present invention relates to a heat transfer device of a network-type heat pipe, wherein the heat transfer is achieved by heat absorption from a heat source, evaporation and condensation of a working fluid fill the device, and the heat dissipates into a heat sink. The capillary pipes forming the heat dissipating unit are made into a network shape, the heat absorbing unit may be constructed in any shape desired for absorbing the heat; and two single capillary pipes are used to connect the heat absorbing unit and the heat dissipating unit.
2. Description of the Prior Art
The conventional heat transfer device of heat a pipe is formed by a pipe, a capillary structure or wick, and a working fluid. In general, a pipes is made of a straight metal tube. The hollow capillary structure made of a porous medium adheres to the inner wall of the tube and forms a hollow channel for the vapor of a working fluid to pass through. The working fluid, such as alcohol, methyl alcohol or water, fills the heat pipe. When one end of the heat pipe (the evaporator) is heated, the liquid working fluid absorbs the heat and evaporates to form a vapor. The vapor then flows out from the capillary structure in the evaporator to another end of the heat pipe (the condenser). The vapor then condenses as a liquid and penetrates the capillary structure in the condenser, while the condensed heat dissipates outwards. The condensed liquid is transferred back to the evaporator through a capillary structure by capillary effect to repeat the process of heating and evaporating and complete a cycle. There are three main defects in the conventional heat pipe: (1) it is made of hard straight tubes so that it lacks flexibility in installation; (2) the use of a capillary structure or porous medium in a heat pipe causes additional cost and quality control problems; (3) the distance of heat transport is limited by the capillary structure.
In order to improve the defects of the aforementioned conventional heat pipe, in the prior art the heat pipe is made as a closed loop and the inner part of the loop has no capillary structure. The loop is mounted vertically with the evaporator at the lower part of a vertical leg and the condenser is mounted at the upper part of another vertical leg. A working fluid, such as alcohol, methyl alcohol or water, fills the loop. When the evaporator is heated, the working fluid absorbs the heat and vaporizes to form a vapor. The vapor then flows to the condenser at the upper part of another vertical leg and condenses as liquid. The condensation heat dissipates outwards to achieve the heat transport, while the condensed liquid flows back to the evaporator by the gravitational force to complete a flow cycle. This kind of heat pipe is call as a "thermosyphon-loop heat pipe", the major defect of which is that the condenser and the evaporator are generally installed on a vertical plane with a short horizontal distance between them so as to minimize the frictional force of the working fluid flowing through the connecting tubes between the two legs.
In order to improve the defects of the conventional heat pipes, in U.S. Pat. No. 4,921,041 (1990) and 5,219,020 (1993), filed by Akachi, Japan, the aforementioned single-loop thermosyphon heat pipe is designed as a multiple-loop capillary heat pipe which is connected in a series to a bundle of parallel capillary pipes. The two ends of the heat pipe are interconnected to form a closed loop. The inner part of the pipe is empty (referring to FIG. 1). An evaporating unit (11) of the multiple-loop capillary heat pipe is on one side and a condensing unit (12) on another side. Heat is transported from the evaporating unit 11 via the condensing unit 12 to the heat sink. The pipe is a designed as capillary tube in order to provide capillary effect. The pipe is filled with working fluid (such as alcohol, methyl alcohol, freon or water) at an appropriate volume ratio. Before operation of the heat pipe, the liquid working fluid is distributed in segments along the multiple-loop heat pipe by capillary effect, and vapor segments fill in between the liquid segments.
As the evaporating unit is heated, the liquid absorbs heat and vaporizes. The vapor bubbles start to grow and the pressure increases so as to push the liquid and vapor segments to flow toward the lower temperature end (condensing unit). The condensation of the vapor in the condensing unit at a lower temperature lowers the pressure and further enhances the apressure difference between the two ends of the evaporating and condensing unit. Because of the inter-connection of the pipe, the motion of liquid and vapor segments in one section of the tube toward the condenser also leads the motion of liquid and vapor segments in the next pipe section toward the high temperature end (evaporator) in the next section. This works as a restoring force. The interaction between the driving force and the restoring force leads to oscillation of the liquid and vapor segments in the axial direction. Therefore, this kind of heat pipe is called a "Pulsing heat pipe" or a "Capillary loop heat pipe". The frequency and amplitude of the oscillation are dependent on heat flow and mass fraction of the liquid in the pipe. There are two defects in this heat pipe: (1) the manufacturing of the capillary loop heat pipe with at least three pipe turns, or several tens or hundreds of turns is difficult and, in particular, the connection between the evaporating unit and the condensing unit is not easy; (2) the whole length of the capillary loop heat pipe must be made from a single capillary tube in order to form a single closed loop (with multiple turns). The design flexibility in practical application is therefore confined.